In an ultrasound machine, a receive beamformer serves two functions: it focuses the receive beam and forms the beam. To focus the beam at any given point in space, the signal received by each element of an ultrasound probe or transducer must be properly combined with the signals from the other elements. This can be achieved by variably delaying the signals from each of the various elements so that the reflections from any given point are correctly summed. Additionally, the delay must be provided on a real-time basis.
Typically, delay (or time-of-flight) values are precalculated and then stored, but this requires significant amounts of memory and an accompanying time requirement for loading this memory. To economize, a subset is stored and the actual values are derived from the stored quantities, but this yields only an approximation. Moreover, the values are fixed with respect to the beam's origin and direction and must be recalculated if the user desires a different set of beam parameters.
Because these numbers are needed at such a rapid pace during an ultrasound examination, the calculations cannot be performed in software as this would be too slow. Thus, if the time-of-flight values are not precalculated and stored in memory, and a high degree of accuracy is desired, some other means must be provided.